Hardline Pro is unlocked after obtaining 40 killstreak rewards (not getting at least a two kill streak 40 times, as some may think). The easiest way to do this is set the player's killstreak to the rewards that require the lowest amount of kills possible. Hardline Pro reduces the number of deaths needed for a deathstreak by 1.

The "Preemptive Strike" title is unlocked by completing Hardline Pro I Challenge. The "Close Support" title is unlocked by completing Hardline Pro VI Challenge along with the perk emblem.

Hardline reduces all killstreak requirements by one. Its Pro version allows the player to re-roll the Care Package killstreak by double-tapping the action button for console versions and the reload key for PC versions, which will change its contents randomly. A Care Package can only be re-rolled once, and will always change its content.

Originally, the SAM Turret, Sentry Gun, and Valkyrie Rockets killstreaks crates could also be re-rolled; however, the December 14, 2010 patch limited Hardline Pro's functionality to the Care Package alone. One also cannot re-roll booby trapped Care Packages, making it easier to tell if one has been hacked.

Below is a table showing the default Care Package probabilities compared to the re-roll probabilities. As can be seen, re-rolling favors middle killstreaks much more than Care Packages, while higher killstreaks are almost unchanged.

Hardline gives the player model medium body armor in the form of Kevlar vest, a helmet on some models and a radio device located on the character's shoulder. However, this particular device is only aesthetic; all players have a radio to call in Killstreaks.

Hardline makes each pointstreak require one less point. This applies to all three strike packages and all of the point streak rewards, even the M.O.A.B.

Hardline Pro is unlocked by obtaining 80 point streak rewards using Hardline. The Pro version has two effects; it reduces the number of deaths required for a deathstreak by one, and it also adds one point to a user's point streak for every two assists earned. Hardline Pro can be easily unlocked when using the Specialist Strike package, as only a single point is needed to earn the first perk.

Hardline returns in Call of Duty: Black Ops II. Hardline increases score earned towards Scorestreak by 20% (not counting UAV, Counter-UAV, Orbital VSAT, or EMP assists). This equates to Scorestreaks requiring 16.7% less score to earn, equivalent to approximately one-to-two less kills to earn a Scorestreak, and even three less kills to earn a Swarm.[1]

Hardline returns in Call of Duty: Ghosts as an Elite perk. It requires two perk points to use and it is unlocked at level 20. Pointstreaks require one less point to obtain, and every two assists counts as a kill towards their killstreak.

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Hardline makes a return in Call of Duty Online as a Tier 1 perk. While equipped, Killstreaks take one less kill to obtain. Within Survival, Cyborg Evacuation and Cyborg Rising, the player is rewarded with a poker, dog tag and battery for each round/wave completed.

The perk is named differently in different languages of the game: in the French version it is "Determination", in Polish it is "Uncompromising" and in Russian the base perk is "Implacability" while the Pro version is "Hard Game Pro".